Liza Sherman has no patience for squares. Not that she's a tie-dye-loving hippie. On the contrary, the soignée septuagenarian can rock a pair of vintage over-the-knee boots with more verve than women half her age. Just don't ask the legendary antiques dealer to explain what she sees in a set of metal chairs made from reclaimed washing machines, or a pair of Portuguese wire eel traps, or an outsize painting of a turtle. And don't admit that you just can't see how they would fit into an interior design scheme. "If I have to explain it, you've lost me," Sherman admits with a laugh. "I don't decorate. I see objects and furniture as shapes, lines, and forms," she says.

For the last 35 years, Sherman has surrounded herself with such idiosyncratic pieces, both in her midtown Manhattan apartment and in her eponymous store, a packed and stacked West Village jewel that bears no signage and is as close to Paris's famous Marché Paul-Bert as it gets. "My home is meant to emulate my shop," she says of the 1,900-square-foot space. In fact, were it not for the prewar elevator, which can't accommodate anything over eight feet, the line between the two might totally disappear.

Sherman knocked down many of the walls in the apartment, which originally had eight rooms, creating a main space that serves as a living area, dining area, and kitchen. The conversion allowed her to do what she does best. "The interior walls prevented me from playing with scale, asymmetry, color, and texture the way that I wanted to, so I had them removed," she says, as if such an undertaking were as natural as waking up in the morning. The renovation had the unintended effect of visually lowering the nine-foot ceilings; applying a swath of flat black paint above and below each "horrible cookie-cutter window" remedied the situation.

Paint, in fact, is as much a design weapon in Sherman's hands as are her esoteric sculptures and furnishings. A single boxy column remains in the center of the main room, a feature most interior designers would insist on disguising. Sherman made it a focal point by turning loose graffiti artists Mint & Serf with a bucket of fire-engine-red paint. The duo applied it in uneven stripes, extending the paint onto the chartreuse floor and across the ceiling, a move that forces the eye to trace its path. It's the walls, however, that reveal the most about Sherman's tradition-be-damned approach. As she watched her painter roll a coat of heavy-duty white primer over the fuchsia that she "couldn't bear for one more day," the lady of the house staged an intervention, forbidding him to smooth away the patterns left behind by the tool's marks. "Perfect surfaces don't interest me," she says in her impeccably tossed-off manner.

Sherman's knack for dodging convention dates to her postcollege years, when, with a Vassar degree and $400, she moved to Manhattan and found a room at her college's New York City club. After a brief stint as a model, she got an interior design degree from Parsons and opened a gallery for promising young artists, including Dan Flavin and Roy Lichtenstein, in a basement space off Fifth Avenue. Her roommate worked for David Rockefeller, who became a frequent customer at the urging of his secretary. "That's when I traded my room for an apartment in the Plaza Hotel," she recalls.

A relationship with artist Liam Ritt changed her life; Sherman calls him the Henry Higgins to her Eliza Doolittle. "He was far more worldly than I was," she says. "Matisse and Picasso were his friends." When he offered her a choice between traveling to Italy or buying a boat, she picked the boat. "It was the only pragmatic decision I've ever made," she jokes. Ritt's influence on Sherman remains evident to this day. "He showed me how to look at objects through an artist's lens," she says.

After spending time as a corporate art advisor—she once convinced a group of Goldman Sachs executives that a collection of Sioux beaded moccasins was worth hanging on a wall—Sherman interned with decorator Billy Baldwin before boredom pushed her to go into business for herself.

In the more than four decades since that she's been buying and selling antiques, she has never strayed far from her artistic proclivities. That explains the agricultural map of France suspended from the ceiling in the kitchen, and, in the study, a dressing-table chair floating on its side. "You'd think it was messy if you didn't know any better," Sherman laughs. Or maybe you'd just be a square.